1. Field of the Invention
The present invention relates to a seal device for sealing a gap between a stationary portion and a rotating body, and to a rotary joint connecting piping formed on a stationary side member and piping formed on a rotation side member to each other to effect delivery of fluid between the stationary side member and the rotation side member. For example, the present invention relates to a dynamic pressure seal device for sending a high pressure coolant liquid or the like into the spindle main shaft of a machine tool rotating at high speed and to a rotary joint device using the same.
2. Description of the Related Art
Nowadays, regarding a spindle device for use in a machine tool, such as a grinding machine, there is a demand for a device which is small and which exhibits a high main shaft RPM from the viewpoint of performing high precision machining and high efficiency machining on a workpiece. However, when the main shaft RPM is high, great machining heat is generated at the machining point where the tool and work are in contact with each other, and this machining heat causes the sharpness of the tool to be lost and hinder the high precision machining. Thus, it is necessary to reliably supply coolant liquid to this machining point to restrain heat generation in the work and tool as a result of machining. However, when coolant liquid is supplied from outside to the tool rotating at high speed, the coolant liquid will be scattered by the centrifugal force, making it difficult for the coolant liquid to reach the machining point. Even if the supply amount of coolant liquid is increased, the cooling of the tool and work is not promoted.
To solve those problems, nowadays, a coolant liquid supply passage is formed inside the spindle main shaft holding the tool, and high pressure coolant liquid is caused to reach the machining point from the interior of the tool. This system is superior in cooling the machining point and is capable of meeting the demand for high precision machining. However, to supply high pressure coolant liquid to the interior of a spindle main shaft rotating at high speed, a high performance rotary joint device is indispensable which is capable of effecting delivery of coolant liquid between the spindle main shaft and the stationary housing supporting its rotation without involving any leakage.
A conventionally known rotary joint device of this type comprises a stationary side member provided on the stationary housing side, a rotary side member which is rotatably supported with respect to the stationary side member through the intermediation of a bearing and which is provided at an axial end of a rotating member such as a spindle main shaft, and a mechanical seal hermetically sealing the gap between the stationary side member and the rotary side member, wherein a recipient hole is formed in the rotary side member along the rotation axis and wherein a supply hole is formed in the stationary side member so as to be opposed to the recipient hole, fluid being blown into the recipient hole from the supply hole.
In this conventional rotary joint device, leakage of fluid from between the stationary side member and the rotary side member is prevented by a contact type mechanical seal, so that in a condition in which the rotary side member rotates at high speed, an intense abrasion is involved, resulting in a rather poor durability. Further, when used for delivery of high pressure fluid, the slide contact portion of the mechanical seal is required to be brought into slide contact with an accordingly high pressure, so that the service peripheral speed must be low, and it is impossible to connect the rotary side member to a spindle main shaft or the like rotating at high speed.
The present invention has been made in view of the above-mentioned problems inherent in the prior art. It is accordingly an object of the present invention to provide a dynamic pressure seal device which can be applied to a rotating body to be rotated at high speed and which is capable of effecting delivery of fluid between the rotary side member and the stationary side member without involving any leakage for a long period of time even when used for delivery of high pressure fluid, and a rotary joint device using the same.
Therefore, a dynamic pressure seal device according to the present invention relates to a seal device for hermetically sealing a gap between a stationary portion and a rotary body, the seal device being characterized by comprising a stationary side member mounted to the stationary portion and a rotary side member mounted to the rotary body, in which the stationary side member and the rotary side member are opposed to each other through the intermediation of a predetermined bearing gap, a lubricant fluid being introduced into the gap to form a dynamic pressure bearing, the gap between the stationary portion and the rotary body being hermetically sealed by the dynamic pressure bearing.
Further, a rotary joint device according to the present invention is a rotary joint device, which connects to each other piping formed in a stationary side member and piping formed in a rotary side member and which performs delivery of a target fluid between the stationary side member and the rotary side member, the joint device being characterized in that: the stationary side member and rotary side member are opposed to each other through the intermediation of a predetermined gap, into which a lubricant liquid is introduced to form a dynamic pressure bearing; the stationary side member has a supply hole opening on the bearing gap of the dynamic pressure bearing and adapted to supply the target fluid to the rotary side member; and the rotary side member has a recipient hole opening on the bearing gap of the dynamic pressure bearing so as to be opposed to the supply hole and adapted to receive the target fluid from the supply hole.
In the rotary joint device of the present invention, constructed as described above, the stationary side member and the rotary side member are opposed to each other through the intermediation of a predetermined gap to form a dynamic pressure bearing, and delivery of target fluid from the stationary side member to the rotary side member is effected through the bearing gap of the dynamic pressure bearing. That is, a supply hole opening on the bearing gap is formed in the stationary side member forming the dynamic pressure bearing, whereas, in the rotary side member, there is formed a recipient hole opening on the bearing gap of the dynamic pressure bearing and opposed to the supply hole, delivery of the target fluid being effected between the supply hole and the recipient hole.
The bearing gap between the stationary side member and the rotary side member constituting the dynamic pressure bearing is as small as several xcexcm. Further, during the rotation of the rotary side member, a high pressure fluid lubricant film is formed in the bearing gap, so that it is possible to prevent, as much as possible, the drive fluid emitted from the supply hole from leaking into the gap between the stationary side member and the rotary side member, that is, into the bearing gap of the dynamic pressure bearing, enabling the total amount of target fluid emitted from the supply hole to flow into the recipient hole of the rotary side member. In other words, the dynamic pressure bearing functions as a seal for preventing leakage of the target fluid. Thus, in the rotary joint device of the present invention, the interval between the stationary side member and the rotary side member is hermetically sealed by a non-contact type seal, so that even under a condition of use in which the rotary side member rotates at high speed, the sealing function is not impaired due to abrasion, making it possible to effect delivery of the target fluid without involving any leakage for a long period of time.
Further, the pressure of the fluid lubricant film formed in the bearing gap of the dynamic pressure bearing is augmented as the RPM of the rotary side member increases, so that the higher the RPM of the rotary side member, the more enhanced the sealing function between the stationary side member and the rotary side member, making it possible to deliver high pressure fluid from the stationary side member to the rotary side member without leakage.
As described above, in the dynamic seal device of the present invention and the rotary joint device using the same, the target fluid is delivered from the stationary side member to the rotary side member through the bearing gap of the dynamic pressure bearing formed by the stationary side member and the rotary side member, and this dynamic pressure bearing functions as a non-contact type seal for preventing leakage of the target fluid, so that even under a condition of use in which the rotary side member rotates at high speed, the sealing function is not impaired by abrasion, and it is applicable to a rotary member to be rotated at high speed. Further, even when used for delivery of high pressure fluid, it is possible to effect delivery of the target fluid between the rotary side member and the stationary side member without involving any leakage for a long period of time.